ABSTRACT The most common cause of inherited blindness is retinitis pigmentosa (RP), a family of diseases with various forms of inheritance caused by mutations in more than 45 genes. Over 100 distinct mutations have been identified in the rhodopsin gene that lead to RP. Many of these mutations cause rhodopsin protein misfolding and retention within the endoplasmic reticulum (ER). The cellular and molecular processes that link rhodopsin misfolding and ER retention to photoreceptor cell death are not well understood. During our previous research period, we investigated the role of the unfolded protein response (UPR) in retinal degeneration. The UPR comprises a set of cellular signaling pathways that detects misfolded proteins in the ER and promotes cell survival by reducing misfolded protein levels. However, if protein misfolding persists, the UPR switches to promote apoptosis. Here, we provide data that mutant rhodopsin linked to RP activates the UPR in vitro and in animal models of RP and that selective manipulation of UPR signaling can prevent cell death in vitro. Based on these findings, we hypothesize that ER stress and UPR signaling play important causal roles in determining photoreceptor cell survival in response to rhodopsin protein misfolding. To test this hypothesis, we will 1) investigate how UPR signaling regulates rhodopsin protein folding; 2) test if we can enhance photoreceptor cell survival in vivo by artificial control of UPR; and 3) determine how mutant rhodopsin expression changes ER structure and morphology in photoreceptors. These studies will provide important molecular, cellular, and genetic insights into the pathogenesis of retinitis pigmentosa arising from mutant rhodopsin expression. These studies may also provide new therapeutic targets to prevent blindness.